Neurosurgeons in China have reported the case of a 24-year-old woman who, after a series of brain scans to investigate dizziness, has just discovered she was born without a cerebellum. This cauliflower-like structure looks like a mini brain (its name is Latin for “little brain”) and it hangs off the back of its bigger brother. The cerebellum, shown on the left in the image above, is estimated to contain half the neurons of the entire brain. Experts used to think its function was purely to do with coordination, balance and controlling the body, but in the last decade or so they’ve realised that its role is far more varied and includes language, emotion, memory and attention.

This revolution in our understanding of the functions of the cerebellum makes it seem all the more remarkable that the woman in question has only just discovered her brain is completely absent this key structure. Certainly, adults who develop illnesses, or incur injuries, that affect the function of the cerebellum (such as cerebellar ataxia) usually suffer profound difficulties with movement, including being unable to stand or walk. Recently its also become apparent that they often have other mental impairments too, in line with the structure’s diverse functions.

Although this woman with no cerebellum apparently started walking late (at age 7), walks unsteadily as an adult and has slurred speech, it’s amazing that she is able to walk and talk at all. The authors of the case study say she has mild intellectual impairment, but they also note that she is married with a daughter, had normal word comprehension and was “fully orientated” by which they presumably mean she had a normal sense of time and place.

“…[T]he functional compensation with the remaining brain tissue is remarkable,” the authors of the case study note in their report. “In our case, complete absence of the cerebellum results in only mild to moderate motor deficiency.” They added: “dysarthria [difficulty speaking] and ataxia [coordination problems], although clearly present, were less than would be expected in completely [sic] absence of the cerebellum.”

This is apparently only the ninth documented living case of “primary cerebellar agenesis”, although the condition was first described in 1831. And while it is amazing that this woman appears to have adapted so well to the absence of such a major brain structure, this is not the first time such claims have been made.

In fact, there was a case reported in 1940, of a man whose lack of a cerebellum was only discovered at autopsy after he died aged 76. Moreover, it was claimed he’d led a relatively symptom-free life. However, this interpretation was challenged in the 1990s. Neuroscientist Mitchell Glickstein noted the lack of information about the man’s life and his neuropsychological profile, and he said it was a “myth” that one could lead a normal life without a cerebellum.

The debate continued with the discovery of more information about the man, including that he’d worked as a manual labourer. Summarizing in 2010, the British experts Roger Lemon and Steve Edgley said there was “potential ammunition for both sides of the debate”, depending in part on whether you take a glass half-full or half-empty interpretation of a patient’s life and symptoms.

This new Chinese case study represents the latest chapter in this ongoing debate. And again, there’s plenty of room for interpretation. Based on the case report, her adaptation to her unusual neuroanatomy is impressive, and it’s yet another example of how well the brain can accommodate extreme challenges, especially when these are present from birth or early in life (other recent case reports involving profound neurological adaptation include an elderly man who just discovered his brain hemispheres are disconnected; and a boy capable of speech even after his entire left brain hemisphere was removed). On a more skeptical note, the lack of detailed information on the Chinese woman’s neuropsychological profile, and the lack of detail about her life (including her employment, schooling and relationships), leaves open the question of how well she has truly coped without a cerebellum.

There are reasons to guard against hyping cases such as this. The overwhelming majority of people who suffer brain injuries and illnesses often face great challenges and difficulties coping with the impairments associated with their conditions. When I was writing my forthcoming book on brain myths, one of the world's leading experts on brain injury, Karen Hux, told me that people who suffer serious brain injury will always have some ongoing deficits. By sensationalising rare cases like this Chinese woman, we risk belittling the seriousness of the vast majority of brain disorders and injuries and generating unrealistic hope about the brain’s plasticity.

On a related but less sober note, cases such as this new Chinese report also reinforce immortal myths about the brain, such as the idea we only use ten per cent of our brains. If a woman can adjust to the absence of so many neurons, the logic goes, then surely most of us are failing to fully exploit our full complement of grey matter. I think balance is the order of the day here. Yes it is incredible that some people are able to adapt so well to unusual brain development or to brain injuries, and it's exciting to think how little we still understand about the way the brain accommodates these challenges, and how we might better learn to exploit this potential. But we should remember that for now there are nearly always serious impairments associated with brain injury and illness (in the case of the Chinese woman, the true extent of her difficulties will likely become clear with further testing), and that there is a significant difference between the brain adjusting developmentally to congenital or early acquired abnormalities, and its ability to adapt to problems encountered later in life.